In some chemical-analysis instruments, the coupling of a liquid chromatograph (LC) to a mass spectrometer (MS) involves an interface that processes the output of the LC to provide suitably ionized sample components for mass analysis by the MS. For example, some interfaces nebulize a fluidic eluent emerging from the LC.
An electrospray interface (ESI), for example, typically directs a chromatographic eluent, including analyte and solvent, through a conductive capillary tube. A charge is transferred from the tube to an aerosol of analyte and solvent that sprays from an exit orifice of the tube. Typically, a neutral carrier gas is mixed with the aerosol to promote evaporation of the solvent and formation of separated ionized analyte molecules suited to mass spectrometric analysis.
ESI and other techniques primarily involve electrostatic nebulization with, or without, pneumatic, thermal, or ultrasonic assistance to form droplets of a liquid stream containing an analyte. The droplets may be generated in a heated or unheated gas stream. The gas serves to desolvate the droplets. The droplets shrink as they desolvate, resulting in the formation of atmospheric ions of the analyte. A portion of these ions are then mass analyzed.
Components of an interface are typically enclosed in a vessel, such as a housing or enclosure, that protects the components and confines chemical vapors. Vapors may include common chromatographic solvents that are mildly hazardous. The vessel typically has a door to provide operator access to components in the vessel for adjustment, maintenance, or repair. Reliable operation of the housing is desirable to avoid exposure of operators to hazardous or irritating vapors.